The present invention relates generally to pressure sensors, and, more specifically, to implantable pressure sensors.
In the medical field pertaining to living patients, pressure sensing of bodily fluids introduces the additional requirement of patient safety. For example, the measurement of blood pressure must not damage the blood itself or form clots therein which are detrimental to patient health.
Artificial heart pumps are being developed in the exemplary form of a Left Ventricular Assist Device (LVAD) which assists damaged hearts. Typical artificial heart pumps are configured for varying blood flowrate, frequency, and pressure as required to meet the typical demands placed on the heart which change in response to work effort. It is therefore desirable to control the heart pump by sensing blood pressure in the body.
In clinical practice, the tricuspid valve between the right atrium and right ventricle is chosen as the reference level for pressure measurement because this is one point in the circulatory system at which hydrostatic pressure factors caused by body position of a normal person usually do not affect the pressure measurement by more than 1 or 2 mm Hg. The reason for the lack of hydrostatic effects at the tricuspid valve is that the heart automatically prevents significant changes at this point by acting as a feedback regulator of pressure at this point.
For example, if the pressure at the tricuspid valve rises sightly above normal, the right ventricle fills to a greater extent than usual, causing the ventricle to pump more blood more rapidly and therefore to decrease the pressure at the tricuspid valve toward zero mm Hg. Thus all clinical blood pressure measurements are gauge pressure measurements referenced to barometric pressure and independent of barometric pressure, and referenced to the tricuspid valve level.
Since the heart pump is preferably fully implanted inside a patient, blood pressure must be also measured inside the body for controlling the pump. However, since it is not practical to directly measure blood pressure at the tricuspid valve, a suitable alternate pressure source must be provided.
Accordingly, it is desired to provide an implantable pressure monitor for measuring blood pressure referenced to outside barometric pressure for controlling a heart pump.
A remote pressure sensor includes a probe having a chamber for holding a liquid. A flexible membrane is mounted in the probe. A conduit joins a reference cell to the chamber for holding the liquid. And, a reference pressure gauge is operatively joined to the conduit for measuring pressure of the liquid therein for use in referencing a primary pressure sensor through which fluid flows.